I would say that you should consider changing what you have, for a couple of different reasons: neither the astro turf or the sand will retain moisture well at all, and since your little guys require a humid environment, thats not good. Another thing to consider is that the hatchlings will want to, and should be able to, burrow and hide alot.
I have heard of folks using Bed-a-Beast, sphagnum moss, peat moss, dirt from their yard combined with any of those, top soil or potting soil, or if you know someone with a wooded lot, go for the real thing and get yourself some leaf mould. Whatever you change to, haveing it about 3 inches deep is a good idea
Sand may be abrasive enough to scratch their little shells, too.
Sphagnum or peat moss can be purchased at any store that has gardening supplies, by the way, and is inexpensive and can be purchased in small quantities: just make sure that any pre-packaged soil or soil amendment you choose does NOT contain any added fertilizers or chemicals.
Stephanie